In situations where joined articles are subject to vibration, it may be desirable to isolate the vibration from passing from any one of the articles to the other. An example of such a situation occurs in motor vehicles with respect to the mounting of a condenser, radiator fan module (commonly referred to in the art as a “CRFM”).
As shown by way of example at FIGS. 1 and 2, a CRFM 10 includes a mounting foot 12 one at each side thereof (only one side being shown in FIG. 1), wherein the mounting foot rests upon a resilient isolator 14, which in turn rests upon a cradle 16 (see FIG. 2). The resilient isolator 14 typically has a washer-like isolator main body 14a, a tubular isolator sleeve 14b integrally connected with, and in normal relation to, the isolator main body, and an isolator central bore 14c (see FIG. 2) extending through both the isolator main body and isolator central bore. An alignment stud 18 of the mounting foot 12 is press-fit into the isolator central bore 14c. One flat engagement surface 14e of the isolator main body 14a abuts the mounting foot 12. The isolator sleeve 14b passes through a cradle hole 16a, and the isolator sleeve has a small enough cross-section relative to the cross-section of the isolator main body 14a such that a second flat engagement surface 14f amply rests abuttingly upon the cradle.
Accordingly, it is seen that the weight of the CRFM 10 is supported by the cradle 16 through the resilient isolator, whereby vibration axially passing between the cradle and each foot is mitigated as it passes through the main body of the respective resilient isolator 14, and vibration transversely (or radially) passing is mitigated by the resiliency of the isolator sleeve 14b. By way merely of exemplification, the resilient isolator 14 is a “compression-style” single-rate resilient isolator, whereby a single resiliency rate is provided as between the cradle and the mounting foot.
In operation, the CRFM may produce fan noise vibration and/or vibrations, wherein from a noise and vibration perspective, it is desired to have a soft resiliency of the resilient isolator in order to decouple these noises and vibrations from passing from the CRFM to the cradle and then through the frame of the motor vehicle, thereby ensuring occupants of the motor vehicle are undisturbed thereby. In operation of the motor vehicle on the road, pavement irregularities produce jarring (or shocking) vibrations, wherein from a ride and handling perspective, it is desired to have a hard resiliency of the resilient isolator in order to prevent the cradle from delivering to the CRFM vibrations which can cause it to shake relative to the body of the motor vehicle.
Accordingly, to accommodate the dual perspectives of noise and vibration isolation and ride and handling isolation, a dual-rate resilient isolator is preferred over a single-rate resilient isolator (as shown at FIG. 1), in that a dual-rate resilient isolator provides a soft resiliency which, initially, isolates noise and vibration of the CRFM from passing to the cradle, and a hard resiliency, subsequently, which retains the CRFM in position with respect to the cradle during episodes of road induced jarring (shocking) vibration.
A dual-rate resilient isolator preferred in the prior art is known as a “shear-style” dual-rate resilient isolator 14′, as for example shown at FIG. 2. The shear-style dual-rate resilient isolator 14′, by way of example, may include a relatively harder resiliency insert material 14d embedded in the relatively softer resiliency material of the isolator main body 14a′, wherein the isolator main body and the isolator sleeve 14b′ are composed of the same softer resiliency material.
In operation, when small amplitude vibrations act upon (in cycles of compression and relaxation) the isolator main body 14a′ between the mounting foot 12 and the cradle 16, the relatively softer resiliency isolator material isolates those amplitude vibrations from passing from the CRFM to the cradle. However, in large amplitude vibrations (in cycles of compression and relaxation), the relatively softer resiliency material of the isolator main body acts in shear with respect to the relatively harder resiliency material of the insert, whereby a hard resiliency response as between the CRFM and the cradle subtends, and thereby prevents the CRFM from shaking relative to the body/frame of the motor vehicle.
From a vehicle performance standpoint, dual-rate resilient isolators are superior to single rate resilient isolators; however, higher cost and investment, and reduced durability are detriments of the dual-rate resilient isolators.
Accordingly, what remains needed in the art is a dual-rate resilient isolator which has low cost and investment, high durability, and excellent vehicle performance.